I ended up calling tech support. The cm said my tickets (purchased from
UT) expired on Aug 12, which was why they were no longer visible. I pointed out that the actual ticket print out has an expiration of Jan 12, 2021. He did more checking, and could definitely see the tickets in his system because he read me the names off of each of them. When I mentioned that the tickets had been purchased from a 3rd party, he said that their system is currently not communicating with the 3rd party retailers. He assured me that once they have an opening date, my tickets will either reappear in the app, or I will be able to rescan them.
Side note: I asked how likely it would be that the expiration on my tickets would be extended once the park reopens, and I was told it was "very likely."